Allotter switch for preassigning idle finder switches



Feb. 6, 1951 a. T. BAKER 2,540,644

ALLOTTER SWITCH FOR PREASSIGNING IDLE FINDER SWITCHES Original Filed Nov. 11, 1944 5 Sheets-Sheet 1 F I6. I

QA T B l L MRA LFM FSM p kl P b co4 50o H Q 4 col MTR RU2 o D RUI lH HI u YB 003 INVENTOR.

GEORGE THOMAS BAKER ATTORNEY Feb. 6, 19 51 3, BAKER 2,540,644

ALLOTTER SWITCH FOR PREASSIGNING IDLE FINDER SWITCHES Original Filed Nov. 11, 1944 -5 Sheets-Sheet 2 INVENTOR. GEORGE THOMAS BAKER ATTORN E Y Feb. 6, 1951 ca. T. BAKER 2,540,644

ALLOTTER SWITCH FOR PREASSIGNING IDLE FINDER SWITCHES Original Filed Nov. 11, 1944 5 Sheets-Sheet 3 INVENTOR. GEORGE THOMAS BAKER mm mav Feb. 6, 1951 T. BAKER 2,540,644

/ALLoTTER SWITCH FOR PREASSIGNING IDLE FINDER SWITCHES Original Filed Nov. 11, 1944 5 Sheets-Sheet 4 INVEN TOR. GEORGE THOMAS BAKER ATTOR NEY G. T. BAKER Feb. 6, 1951 ALLOTTER SWITCH FOR PREASSIGNING IDLE FINDER SWITCHES 5 Sheets-Sheet 5 Original Filed NOV. 11, 1944 INVENIUR. GEORG E THOMAS BAKER iZQ ATTORNEY Patented Feb. 6, 1951 TENT GFFI-CE ALLOTTER SWITCH FOR PREASSIGNING IDLE FINDER SWITCHES George Thomas Baker, Liverpool, England, as-

signor to Automatic Electric Laboratories, Inc Chicago, IlL, a corporation of Delaware Original application November 11, 1944, Serial No. 562,940. Divided and this application August 3, 1948, Serial No. 42,164. In Great Britain September 16, 1944 4' Claims.

The present invention relates in general to telephone systems, and mor particularly to automatic telephone systems employing finder switches for connecting calling lines to numerical switches.

This application is a division of the application Serial No. 562,940, filed November 11, 1944, now Patent No. 2,508,636, dated May 23, 1950.

It is an object of the invention to provide in a telephone system of the character described, new and novel circuit means for accomplishing the various connections.

Another object of the invention is to provide improved means for pre-assigning idle line-finders whereby an assigned line-finder is allotted sufficient time in a new and novel manner for finding a calling line before th line-finder allotter pro-assigns another line-finder, and whereby the line-finder allotter passes over a linefinder in prior use at an increased rate of speed.

A feature of the invention resides in the new and novel arrangement wherein a certain number of terminals of the line-finder allotter are associated with a pre-assigned line-finder, and wherein means is provided for causing the linefinder allotter to successivel test said numberof terminals in order that the pro-assigned linefinder will have sufficient time to find a calling line before the line-finder allotter pre-assigns another line-finder.

There are other objects and features of the invention having to do forthe most part with details in carrying out the foregoing. The Various objects and features of the invention will be-understood best uponthe perusal of the following description of the accompanying live sheets of drawings which show a preferred embodiment of the invention.

The embodiment illustrated in the drawings relates to an improved and simple telephone system suitable for rural areas, and which will operate over any subscribers line which is good enough to enable manual signalling to be performed-,i. e., good enough to enable a relay at an exchange to be operated or released.

Use is made of the automatic selecting principle disclosed inthe application of Reginald Taylor and George Thomas Baker, Serial No. 537,564 filed May 27, 1944, now Patent No. 2,421,169, dated May 2'7, 1947, which does not necessitate reception of dialled impulses or the like from a calling point, the selection of any one of a number of lines being initiatedin response to a signalfrom a calling point, and proceeding until terminated by a further signal from the calling point when the desired line is encountered, the progress of the selecting operation being indicated continuously at the calling point, for instance audibly.

In the subscribers telephon instruments, which in the ensuing circuit description are assumed to be of the magneto type, a single-break push key short-circuited by a condenser is inserted in series with the lin and may be fitted, if required, external to the telephoneeither as a wall mounting or as a loose cord connected item lying on a desk. This unit requires very little maintenance and that of an almost unskilled nature.

The exchange i called by lifting-the handset and turning the generator, whereupon at the end of the alternating current generation a finder/connector link is caused to associate itself with the calling line and is then held from the calling partys loop. Certain type of telephones might require a minor wiring modification to ensure this procedure being efiective. The receiver is then placed to th ear and the signalling button is depressed. Short pulses of tone which are delivered from the link as its connecting switch performs its selecting operation are now heard in the receiver and these are counted until a number corresponding to the Wanted line has been heard. The button is then released and ringing tone or busy tone will be heard exactly as in normal automatic working. The pulses are sent out at a comparatively slow rate so that no difficulty is experienced in stopping the connector at the appropriate point. This method will function quite satisfactoril on loops of up to 3000 ohms, and since the usual A, B and C dialling relays are unnecessary and the magnets have ample time to energize, the system is very robust.

Referring now to the drawings,

Fig. 1 shows a line circuit for a telephone station equipped with a magneto telephone instrument.

Figs. 2 and 3 when arranged. side by side together show the circuit of the common equipment required for allotting the various finderconnector link circuits.

Figs. 4 and 5 when arranged side by side to gether show the details of a finder-connector link circuit.

It should be understood at this time that while the embodiment of the present invention disclosed and described in this specification includes switches of the well-known 25-contact rotary lineswitch type, the invention is not limited to the particular form shown but may utilize; larger bank-capacity switches to increase the number of station lines. It should b further understood that while a plurality of battery connections are shown in the drawings, they are preferably the same battery.

Considering now the detailed circuit operation,

typical values for certain relay windings and resistors are given for general guidance, the supply voltage being assumed to be 50 volts. Referring first to the subscribers line circuit of Fig. 1, when the subscriber lifts his receiver to loop his line SL and then turns the handle of the generator, relay RU, which is responsive to alternating current by virture of capacitor QA and rectifier MRA, is operated and operates relay L but prevents its contacts being effective. When the ringing has ceased, the line SL remains looped and relay L remains locked Via contacts L2 and common lead H to a battery-connected start relay SS in the common equipment, Figs. 2 and 3, this circuit extending a start condition to the common equipment which causes a link line finder to hunt for the battery marking placed on the P bank in the finder multiple LFM by contacts Ll. When the finder reaches the line, relay CO is energized over the P conductor and disconnects relay L and extends the line SL- through to the link.

On an incoming call, relay CO is operated directly over the connector multiple FSM from the P normal lead to disconnect relay RU. The ecohm resistance across CO is to ensure the quick and efiective action of the switching relay in the calling link.

Considering new the common equipment of Figs. 2 and 3, the allotter uniselector AL, Fig. 2, which gives access to up to eight links, will be normally resting on a free link since the earth extended back from busy links over leads such as I2 causes the uniselector magnet ALlvi to selfdrive via interrupter contacts ALMC over busy outlets, each of which connects with three successive contacts on the AL switch banks. If all the links are busy, earth is removed from the overflow common l3 and so causes the uniselector AL to rest on the last contact.

lhe operation of relay SS from a calling line circuit extends an earth via bank ALE to cause 'the preselected link to hunt for the calling line.

Relay SS at contacts SS i also causes the rhythm relay RR, oi the type disclosed in British Patent No. 518,877 to swing across and make its single pair of contacts. This energizes relay PU which at contacts PUE completes a circuit from earthed lead I3 for the allotter magnet ALM and at contacts PU! energizes relay RS which at contacts RSI locks up and breaks the original pull-over circuit of relay RR and at contacts RS2 gives it a pulse in the reverse direction to cause it to swing back and so to break the circuit of relay PU. The swinging action of relay HR is timed at .75 of a second and at each swing a pulse is given to uniselector magnet ALM and also to the rhythm relay itself to keep it swinging. Hence, in not less than 1.5 seconds the ailotter will move 01f the selected link. This time is surficient for the link finder to make one complete revolution, and finding should be achieved by that time. If not, this indicates a fault condition and the need for a second link to be automatically started up which occurs when the allotter steps to the next link. If this or any succeeding link is busy, it is passed over rapidly by self-interrupted stepping. If finding does not take place normally, earth is i extended on to bank ALI from the link and causes the allotter to move on to the next outlet.

The rhythm relay RR, by the intermediary of relay PU, also controls the stepping of the time pulse uniselector TP, Fig. 3. This stepping is initiated on the operation of relay T? from a start condition over lead l5 from the link circuit and is subsequently effected by means of contacts PUE and TF5. Jhile switch TP is in the home position, earth is applied by wiper TPl to the S pulse lead it and in stepping at the rate of one step per .75 second wiper Ti ireaches the Z pulse contact 4% extending to the lead i: after 48 steps, 1. e. 36 seconds. Relay '1"? at contacts TP l also provides th ringing and tone start by energizing the ringing vibrator relay VB and the busy tone relay BT, while at contacts T1 2 it maintains the RR, PU and RS interacting circuit independently of contacts SS5.

An S pulse is a ground application to lead it by way of wiper TPi (Figure 3) when the time pulse uniselector is in the home position, and is for the purpose of operating relay ATS of the hunting finder by way of contacts AFR! when the finder wiper ALF5 has seized the calling line and thereby caused the operation of relay AFR. Relay ATS applies ground potential to lead i5 by way of contacts ATSZ to operate relay TP, and relay TP through contacts TF5 and PUii completes an operating circuit to magnet TPM which is time controlled by the interaction of RR, PU and An S pulse may, therefore, be considered as a starting pulse for the time pulse uniselector (Figure 3). A Z-pulse is a ground application delivered by way of contacts TF3 (Figure 3) when wiper TPG has reached contact position ii and is for the purpose of causing relay ATZ cf the occupied finder to thereupon operate. If the calling subscriber fails to signal by this time, or if the called subscriber has not answered by this time, relay ATZ in operating will open the holding circuit of finder relay AFH at contacts ATZl, thereby causing a forced release. A Z-pulse may, therefore, be considered as a pulse which terminates a predetermined time interval for causing a forced release under the conditions outlined in this paragraph.

Vibrating relay VB in known manner supplies ringing current to the continuous ringing lead 22, while relay BT supplies number unobtainable tone to lead 18. Furthermore since the switch TP steps once every .75 second alternate contacts on banks TF3 and TPB can be used to break up the continuous tone provided by relay BT into the off and on tone used for busy, which is applied to common lead l9. Contacts PU i and wipers and banks TPZ and 'I'P5 operate relay IR for two brief periods of approximatel 0.3 second in each three second cycle, and this relay at contacts IRl provides a verification tone over common lead 24 and at contacts 1R2 provides interrupted ringing current over common lead 2i and also interrupted ringing tone via capacitor QD over common lead 20.

Referring now to the link circuit of Figs. 4. and 5, when the link is seized from the allotter by the extension of earth over lead it, relay ASS is energized and thereupon at contacts ASSl provides a testing circuit for relay AFH, at contacts ASS2 provides a driving circuit for the line finder switch magnet ALFM and at contacts ASS3 brings up relay AA. Relay AA in operating, at contacts AAI, Fig. 5, causes rhythm relay ARR to swing its armature away from its contacts ARRI, as distinct from relay RR in Fig. 2 which t closedits contacts on energization, and at contacts AA2 brings uprelay AE from either of the two home positions i] or l2 of the connector switch bank AFSA. Relay AE, in ope ating, at contacts AE3 prepares an operating circuit for relay APU.

When the finder switch ALF reaches the calling line which is marked b battery potential on bank ALF by way of resistor YA and relay 00, Fig. 1, relay AFl-I energizes over its two windings in series and thereupon at contacts AFHZ applies guarding and, holding potential to the outlet seized, while at contacts AFH: it brings up relay AFR and disconnects the switch driving circuit. Relay AFR in operating, at contacts AFRl and AFR3 switches through the speaking conductors to relay AA, at contacts AFR2 disconnects earth from the overflow common lead l3 and also applies earth to lead l2 so as to step the allotter switch in the common equipment on to another free link in readiness for further calls, at contacts AFR5 completes an alternative holding circu-it for relay AE, at contacts AFR? energizes relay ATS from the time pulse S lead I5 and at contacts AFRii disconnects relay ASS. Thereupon at contacts ASSS the local holding circuit for relay AA is opened, but this relay now remains held over the calling partys loop. Relay ATS, in operating, locks over its. upper winding and, at contacts ATS2 applies earth to the time pulse and ringing current and tone generation start lead I 5, while at contacts ATS3 it connects relay ATZ on to the Z lead ll.

When the subscriber operates his signalling button to initiate the selecting operation, the direct current calling loop is opened and relay AA releases, whereupon at contacts AAi relay ARR is allowed to swing back and make its contacts ARR] thus operating relay APU. Relay APU in operating, at contacts APUI energizes the connector switch magnet ARSM and at contacts APU2 gives a small energization to relay ARR to ensure the continuation of the swinging movement, while at contacts APU3 it extends number unobtainable tone via common lead It and the windings of relay AA to the calling party, this tone being utilized for selective signalling purposes. When rhythm relay ARR opens its contacts, relay APU releases and de-energizes the connector switch magnet and at the same time opens the tone circuit, the subscriber having received a pulse of tone corresponding to one step of the connector switch. Relay APU in releasing de-energizes relay ARR which thereupon swings back to reclose its contacts ARRI and the cycle of operations thus repeats itself, the calling subscriber receiving a tone pulse for each step of the connector switch. Immediately the connector switch leaves its home position, wiper AFS4 extends earth via contacts AH5 and AE5 to bring up relay AER, and this relay at contacts AER! prepares for the short-circuiting of relay AE, at contacts AERS locks itself and at contacts AERB prepares a testing circuit for relay AH. When the signalling button is released after a number of tone pulses have been received appropriate to the number required, relay AA reoperates and at contacts AAI opens any further circuit for relay APU and so halts the stepping, while at contacts AA2 it short-circuits relay AE which commences to release slowly. During the release time of relay AE, a testing circuit is completed via contacts AAl, AERB, AEE and AFRS for relay AH over wiper and bank AFS5 on to the P normal lead of the called subscriber.

If this subscriber is free, relay AH energizes in series with the called subscribers cut-off relay CO and resistor YA, Fig. 1 and on the release of relay AE initiates ringing or the. called partys bell via common lead 2i and relay AF, a return circuit being completed via resistor AYB and lead 30 to battery, while at contacts AH2 ringing tone from common lead 20 is supplied to the calling party.

When the calledparty replies, relay AF operates to trip the ringing and switch the speaking leads through, whereupon relay AD operates over the called partys loop in series *with the differential relay APC which is non-operative in this condition. Relay AD in operating, at contacts AD2 and ADS opens the time pulse circuit for relay ATS and at contacts ADi opens the circuit of relay AER which on restoring after its slow period at contacts AERA opens the ringing tone circuit and at contacts AER5 extends earth for metering from wiper and bank AFS4 over contacts AH E to the M lead of the calling partys line circuit.

If the called subscriber is busy when the conhector ccmes to reston his line, relay AH will fail to operate during the release period of relay AE and hence on the release of relay AE, busy tone will be returned to the calling party via lead it contacts AI-I2, AERe and AE2.

Considering now the various possible release ccnditions for the link, if the calling party hangs;

without signalling, this is equivalent to operating but not releasing the signalling button. Under this condition the connector switch continues to step until it arrives at its next home position, say !2 in this instance, whereupon a cir-- cuit is completed to shunt down relay via. wiper and bank AFSI! and contacts AERE, AEE and AFRG. Relay AFH, in releasing, releases: relay AFR which brings down relays AE and AER and all relays are then normal.

Under normal release conditions, when the calling party hangs up, relay AE will already be normal so that relay AA in releasing will bring down relay AF'H by short-circuiting via contacts AAi, ARE and AFR l. Relay AFH, in releasing, brings down relay AFR which then releases relays AH, AF and AD. On the release of relay AH, a self-interrupted circuit is completed for magnet AFSM over wiper AFSG, and the connector switch is advanced to its next normal position. In case the called subscriber hangs up first, relay AD in releasing will at contacts ADE extend a short-circuiting earth back via contacts AFRE, ADE, AER3, AF! and AFRA to relay AFH with similar results as for the calling party release. 7

Under time pulse releaseconditions, ii the calling subscriber has failed to signal by the time the Z pulse is received over lead ll, or if the called subscriber has not answered in this time, relay ATZ in operating will release relay AFH at contacts A'IZl, and. the other relays then release in turn.

It should be understood that while one embodiment of the invention is disclosed and described in this specification, the invention is not limited to the particular form or application shown, but is entitled to the equivalents thereof within the scope of the appended claims.

What is claimed is:

1. In a telephone system, lines, idle finders having access to said lines, a source of potential, a progressively movable automatic allotter switch having a contact bank, the contacts or said bank being divided into groups of adjacent contacts, each of said groups of contacts corresponding to one of said finders, means for causing said allotter to pre-assign an idle finder, said allotter stopping on the first contact of said group corresponding to said pre-assigned finder, means responsive to the initiation of a call over one of said lines for causing said pre-assigned finder to hunt said. calling line, means responsive to said initiation of said call for stepping said allotter from said first contact successively to the remaining contacts of said one group at a predetermined rate while said pre-assigned finder is hunting said calling line, said rate of :stepping of said allotter permitting said hunting finder to test all said lines, if necessary, before .said allotter reaches the last contact of said one group, means responsive to said hunting finder finding said calling line for causing said hunting finder to seize said calling line, means responsive to said seizure of said calling line for connecting said potential to the last contact of said one group, and means responsive to said allotter contacting said potential for causing said allotter to pre-assign another idle finder.

2. A telephone system as claimed in claim 1 and means for stepping said allotter over the contacts of a group corresponding to an occupied finder at a faster rate than that at which said allotter is stepped over the contacts of said one group corresponding to said first mentioned preassigned finder.

3. In a telephone system, lines, idle finders having access to said lines, a progressively movable automatic allotter switch having a contact bank, the contacts of said bank being divided into groups of adjacent contacts, each or" said groups of contacts corresponding to one of said finders, means for causing said allotter to preassign an idle finder, said allotter stopping on the first contact of said group corresponding to said pre-assigned finder, means responsive to the initiation of a call overone of said lines for causing said pre-assigned finder to hunt said calling line, means responsive to said initiation of said call for stepping said allotter from said first contact of said one group across the remaining contacts of said one group at a predetermined uniform rate while said pre-assigned finder is hunting said calling line, said rate of stepping or" said allotter making it possible for said hunting finder to complete a full hunting cycle of all said lines before said allotter reaches the last contact of said one group, means responsive to said allotter reaching the last contact of said one group after said hunting finder has completed a full hunting cycle and failed to find and seize said calling line for stepping said allotter from the last contact of said one group, and means for disabling said hunting finder in response to said allotter stepping from the last contact of said one group.

4. The telephone system claimed in claim 3 together with means responsive to said allotter stepping from the last contact of said one group for causing said allotter to assign another idle finder to hunt said calling line.

GEORGE THOMAS BAKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,256,500 Clausen Feb. 12, 1918 1,456,567 Lundell May 29, 1923 1,600,358 Puckette Sept. 21, 1926 1,799,485 :Stehlik Apr. 7, 1931 2,421,169 Taylor May 27, 1947 

